On 28/07/2014 02:19, Nightjar "cpb"@ insert my surname here wrote:
On 28/07/2014 01:23, Dave Liquorice wrote:
On Sun, 27 Jul 2014 23:46:14 +0100, Tim Watts wrote:

If I move into very hypothetical areas, I could possibly see a
move to
have residential areas supplied at 50v or less, under the elfen
safety
banner.

That's going to be a big cable to my 3kW kettle and heater ;-)

Even bigger for 10 kW of storage heating... 40 odd amps at 230 V for
a few hours makes the tails warm. The 200 A required for a 50 V
supply is getting hard to handle.


For a H&S viewpoint, an ELV domestic system would save around 20-25
domestic deaths and around a third of a million serious injuries from
electrocution every year.

Although you would likely burn/smoke that many to death instead ;-)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

charles wrote:

If I move into very hypothetical areas, I could possibly see a move to
have residential areas supplied at 50v or less, under the elfen safety
banner.

But you'd get absurdly high currents.


That would fit nicely into the modern mindset then. Absurdity is all the
rage when it comes to h & S.

Bill

Nightjar "cpb"@ insert my surname here wrote:

For a H&S viewpoint, an ELV domestic system would save around 20-25
domestic deaths and around a third of a million serious injuries from
electrocution every year.


Is that in Doncaster, nationally, or world wide?

Bill

On 28/07/2014 03:43, Bill Wright wrote:
Nightjar "cpb"@ insert my surname here wrote:

For a H&S viewpoint, an ELV domestic system would save around 20-25
domestic deaths and around a third of a million serious injuries from
electrocution every year.


Is that in Doncaster, nationally, or world wide?


That is the number of deaths and serious injuries in the UK every year.
Around 2.5 million people in the UK also receive a mains voltage
electric shock every year.

--
Colin Bignell

"David Paste" wrote in message
...
Hello all.

The world has a few differing domestic electrical standards, 100, 120,
240 volts, 50 and 60 Hz and so on. Industrial customers have yet more.

Distribution via high voltage AC, and now DC in places.

I understand why various areas of the world have these differences - due
to historical reasons, etc.

My question is that if we were to have a brand new electrical system,
common to all areas, what would, or could, it be? Still AC? 300 volts?
Different frequency?

No real reason to ask other than idle curiosity.


There's no complete answer as it depends on the size of the system.
Higher voltage reduce transmission losses.
DC reduces transmission losses too. (But requires more technogly)
Higher frequncys increases losses but makes more compact motors and
transformers possible.

We are in the midst of a technological evolution when our powers systems
will be linked to others abroad far more than at present, micro generation
will be universal and we will have smart grid technology to control
everything.

On 28/07/14 02:19, Nightjar "cpb"@ insert my surname here wrote:
On 28/07/2014 01:23, Dave Liquorice wrote:
On Sun, 27 Jul 2014 23:46:14 +0100, Tim Watts wrote:

If I move into very hypothetical areas, I could possibly see a
move to
have residential areas supplied at 50v or less, under the elfen
safety
banner.

That's going to be a big cable to my 3kW kettle and heater ;-)

Even bigger for 10 kW of storage heating... 40 odd amps at 230 V for
a few hours makes the tails warm. The 200 A required for a 50 V
supply is getting hard to handle.


For a H&S viewpoint, an ELV domestic system would save around 20-25
domestic deaths and around a third of a million serious injuries from
electrocution every year.


How many would then die from fires caused by wiring problems?

"Nightjar "cpb"@" "insert my surname here wrote in message
...
On 27/07/2014 22:24, newshound wrote:
On 27/07/2014 21:40, wrote:
Nightjar wrote:
AC for simple long-distance transmission...
Except for underwater cables, where it can cause unacceptable
transmission losses.

How does immersing a 11kV AC cable in water increase transmission
losses? This isn't a joke question, I can't see how the medium
surrounding a cable changes the action of the cable itself, other
than cooling effects.

jgh

It's losses in the dielectric, so it applies to underground cables too.
Dielectric losses in air are low.

Like the man says, although the problem is significantly greater under
water. 30km is about the limit for AC transmission under water, which is
why our links to the continent are HVDC. Even then, the cables are very
specialised and there are IIRC only three manufacturers of HVDC underwater
cables in the world. That is a limiting factor on how many offshore wind
farms can be built, as they need HVDC underwater cable, the manufacturers
have a limited capacity and well filled order books, while increasing
capacity is not something that can be done overnight.


Our main link to Europe is not underwater, it is via the channel tunnel.
http://www.independent.co.uk/news/bu...l-2289665.html

On 28/07/14 02:04, The Natural Philosopher wrote:
On 27/07/14 23:46, Tim Watts wrote:
On 27/07/14 22:24, Nightjar "cpb"@ insert my surname here wrote:
If I move into very hypothetical areas, I could possibly see a move to
have residential areas supplied at 50v or less, under the elfen safety
banner. There would also be an advantage to choosing a lower frequency,
which would reduce transmission losses (around 12% at lower voltages).
The flicker effect of a lower frequency could be overcome by mandating
only high frequency fluorescents or all LED lighting.


That's going to be a big cable to my 3kW kettle and heater ;-)

There's something to be said for higher voltage = lower current and a
lower risk of fires.

its about power not current

High current = risk of terminations becoming hot and starting a fire.

High current = larger cables that are more difficult to terminate properly.

On 28/07/2014 02:06, The Natural Philosopher wrote:
On 27/07/14 23:49, Tim Watts wrote:
I thought it was more the issue that you cannot phase lock France and
the UK? So DC is a natural choice if you have to re-invert it. And if
you have to do that, might as well transmit in DC too.

Not saying your reason is not a good reason - I just thought it was a
secondary reason to a fairly immutable primary problem.

No. I visited the first link to france at the UK end and the issue is
primarily one of losses

'we can draw an arc for 30 minutes off the capacitance in that cable'

To drive that capacitance takes a LOT of out of phase current and that
suffers resistive losses.

Big ones

The main AC losses are inductive and leakage by capacitance to ground,
not resistive.

That's what they told me when I took a group of trainee electrical
engineers to the site a few decades ago. The guy was actually quite
surprised when none of them could answer the question he asked of why
they did it the way they do, but the coach driver could.

Assuming the power *could* be usefully transmitted that far through an
underground/ undersea cable, it wouldn't be much harder to lock the
English and French grids than it is to lock the French, German, Italian
and so on grids.

--
Tciao for Now!

John.

On 28/07/2014 01:56, The Natural Philosopher wrote:
On 27/07/14 22:24, newshound wrote:
On 27/07/2014 21:40, wrote:
Nightjar wrote:
AC for simple long-distance transmission...
Except for underwater cables, where it can cause unacceptable
transmission losses.

How does immersing a 11kV AC cable in water increase transmission
losses? This isn't a joke question, I can't see how the medium
surrounding a cable changes the action of the cable itself, other
than cooling effects.

jgh

It's losses in the dielectric, so it applies to underground cables too.
Dielectric losses in air are low.

No it really isn't dielectric losses.


It's capacitive loading. The capacitance per kilometre of overhead lines
between cable and ground is low, while the capacitance per kilometre of
underground cables is at least two orders of magnitude higher.

At the lengths of cable used for power distribution, some of the effects
that normally only affect HF signals come into play at 50Hz.

--
Tciao for Now!

John.

Bill Wright wrote:
charles wrote:

If I move into very hypothetical areas, I could possibly see a move
to have residential areas supplied at 50v or less, under the elfen
safety banner.

But you'd get absurdly high currents.


That would fit nicely into the modern mindset then. Absurdity is all the
rage when it comes to h & S.

Bill
And think of the size of the appliances and motors etc and the cost of
the copper and the overall resources

On 28/07/2014 02:03, The Natural Philosopher wrote:
On 27/07/14 22:45, tony sayer wrote:
In article ,
scribeth thus
Nightjar wrote:
AC for simple long-distance transmission...
Except for underwater cables, where it can cause unacceptable
transmission losses.

How does immersing a 11kV AC cable in water increase transmission
losses? This isn't a joke question, I can't see how the medium
surrounding a cable changes the action of the cable itself, other
than cooling effects.

jgh

Inductive and Capactive losses theres some stuff on the AAB website
somewhere;!...

Not sure that induction plays any part..

Transmission lines have a calculable inductance per metre, and as the
length approaches infinity, so does that inductance.

There is a characteristic impedance for transmission lines, which
affects both transmission and losses.

Seek ye here!...


http://new.abb.com/about/technology/dc-portal





--
Tciao for Now!

John.

"The Natural Philosopher" wrote in message
...
On 27/07/14 23:49, Tim Watts wrote:
I thought it was more the issue that you cannot phase lock France and
the UK? So DC is a natural choice if you have to re-invert it. And if
you have to do that, might as well transmit in DC too.

Not saying your reason is not a good reason - I just thought it was a
secondary reason to a fairly immutable primary problem.

No. I visited the first link to france at the UK end and the issue is
primarily one of losses

'we can draw an arc for 30 minutes off the capacitance in that cable'

To drive that capacitance takes a LOT of out of phase current and that
suffers resistive losses.

Big ones


Drivel
Capacitance does not cause any losses.
It does cause phase shift and instability.
When the cable is under load it will actually help with phase shift.
Only resistance causes losses.

Where exactly is this arc drawn for 30 minutes and for what purpose.?

On 28/07/2014 08:13, Tim Watts wrote:
On 28/07/14 02:19, Nightjar "cpb"@ insert my surname here wrote:
On 28/07/2014 01:23, Dave Liquorice wrote:
On Sun, 27 Jul 2014 23:46:14 +0100, Tim Watts wrote:

If I move into very hypothetical areas, I could possibly see a
move to
have residential areas supplied at 50v or less, under the elfen
safety
banner.

That's going to be a big cable to my 3kW kettle and heater ;-)

Even bigger for 10 kW of storage heating... 40 odd amps at 230 V for
a few hours makes the tails warm. The 200 A required for a 50 V
supply is getting hard to handle.


For a H&S viewpoint, an ELV domestic system would save around 20-25
domestic deaths and around a third of a million serious injuries from
electrocution every year.


How many would then die from fires caused by wiring problems?

The biggest cause of electrical fires is overloading of circuits. As we
are not upgrading any existing system, but are starting from scratch and
designing everything anew, with the benefit of present knowledge, we
could build everything to accept heavier overloads and to have much
greater and localised integral overload protection. The result could
well be a reduction in deaths from electrical fires.

--
Colin Bignell

On 28/07/2014 08:16, harryagain wrote:
"Nightjar "cpb"@" "insert my surname here wrote in message
...
On 27/07/2014 22:24, newshound wrote:
On 27/07/2014 21:40, wrote:
Nightjar wrote:
AC for simple long-distance transmission...
Except for underwater cables, where it can cause unacceptable
transmission losses.

How does immersing a 11kV AC cable in water increase transmission
losses? This isn't a joke question, I can't see how the medium
surrounding a cable changes the action of the cable itself, other
than cooling effects.

jgh

It's losses in the dielectric, so it applies to underground cables too.
Dielectric losses in air are low.

Like the man says, although the problem is significantly greater under
water. 30km is about the limit for AC transmission under water, which is
why our links to the continent are HVDC. Even then, the cables are very
specialised and there are IIRC only three manufacturers of HVDC underwater
cables in the world. That is a limiting factor on how many offshore wind
farms can be built, as they need HVDC underwater cable, the manufacturers
have a limited capacity and well filled order books, while increasing
capacity is not something that can be done overnight.


Our main link to Europe is not underwater, it is via the channel tunnel.
http://www.independent.co.uk/news/bu...l-2289665.html


That is a quarter of the capacity of the Sellindge to Les Mandarins
underwater link and they were still only talking about it in April this
year.

--
Colin Bignell

In article ,
Nightjar \cpb\@ insert my surname here wrote:
On 28/07/2014 01:23, Dave Liquorice wrote:
On Sun, 27 Jul 2014 23:46:14 +0100, Tim Watts wrote:

If I move into very hypothetical areas, I could possibly see a
move to
have residential areas supplied at 50v or less, under the elfen
safety
banner.

That's going to be a big cable to my 3kW kettle and heater ;-)

Even bigger for 10 kW of storage heating... 40 odd amps at 230 V for
a few hours makes the tails warm. The 200 A required for a 50 V
supply is getting hard to handle.


For a H&S viewpoint, an ELV domestic system would save around 20-25
domestic deaths and around a third of a million serious injuries from
electrocution every year.

but the higher currents involved could easily cause greater fire hazards -
so an increase in fatalities .

--
From KT24

Using a RISC OS computer running v5.18

harryagain wrote:

Our main link to Europe is not underwater, it is via the channel tunnel.

"IS" are you sure?

http://www.independent.co.uk/news/bu...l-2289665.html

I read lots of "PLANS", "PROPOSED", "WILL" and "COULD". Facts harry, you
should try some ...

ElecLink doesn't even seem to have started yet, and may never do

http://www.ft.com/cms/s/0/2f563bce-9e1a-11e3-b429-00144feab7de.html#axzz38kOXxdkI

Proposed capacity is 1000MW (doubled from the initial 500MW capacity you
linked to), isn't the existing French connector 2000MW, and the existing
Dutch connector 1000MW, how would that make it the main link?

Seems they have greased enough palms as rules have now been bent for them

https://www.ofgem.gov.uk/ofgem-publications/87163/eleclinkdecisioncoverletter.pdf

In article , The Natural Philosopher
scribeth thus
On 27/07/14 22:45, tony sayer wrote:
In article ,
scribeth thus
Nightjar wrote:
AC for simple long-distance transmission...
Except for underwater cables, where it can cause unacceptable
transmission losses.

How does immersing a 11kV AC cable in water increase transmission
losses? This isn't a joke question, I can't see how the medium
surrounding a cable changes the action of the cable itself, other
than cooling effects.

jgh

Inductive and Capactive losses theres some stuff on the AAB website
somewhere;!...

Not sure that induction plays any part..


Wouldn't have thought it would be but the article alluded to was very
comprehensive as to the reasons why it was a problem...

Seek ye here!...


http://new.abb.com/about/technology/dc-portal




--
Tony Sayer

In article , Andy
Burns scribeth thus
harryagain wrote:

Our main link to Europe is not underwater, it is via the channel tunnel.

"IS" are you sure?

http://www.independent.co.uk/news/bu...r-link-to-run-
through-channel-tunnel-2289665.html

I read lots of "PLANS", "PROPOSED", "WILL" and "COULD". Facts harry, you
should try some ...

ElecLink doesn't even seem to have started yet, and may never do

http://www.ft.com/cms/s/0/2f563bce-9...ml#axzz38kOXxd
kI

Proposed capacity is 1000MW (doubled from the initial 500MW capacity you
linked to), isn't the existing French connector 2000MW, and the existing
Dutch connector 1000MW, how would that make it the main link?

Seems they have greased enough palms as rules have now been bent for them

https://www.ofgem.gov.uk/ofgem-publi...ncoverletter.p
df


This is how we're going to get around power shortages in the UK look too
that forward thinking country France and pipe their nuclear power in by
that tunnel!..

Now we know the real reason why it was built, perhaps theres a 4th bore
there somewhere;?....
--
Tony Sayer

Tim Watts wrote:

High current = larger cables that are more difficult to terminate properly.

and much more expensive, so people are likely to scrimp and use
under-specced extensions ...

On 28/07/2014 09:47, Andy Burns wrote:
Tim Watts wrote:

High current = larger cables that are more difficult to terminate
properly.

and much more expensive, so people are likely to scrimp and use
under-specced extensions ...



The logical extension of those arguments is to put 11kV straight into
the house :-)

--
Colin Bignell

On Monday, July 28, 2014 8:22:28 AM UTC+1, F Murtz wrote:
Bill Wright wrote:
charles wrote:

If I move into very hypothetical areas, I could possibly see a move
to have residential areas supplied at 50v or less, under the elfen
safety banner.

But you'd get absurdly high currents.

That would fit nicely into the modern mindset then. Absurdity is all the
rage when it comes to h & S.

And think of the size of the appliances and motors etc and the cost of
the copper and the overall resources

Extra resource use would translate to less NHS funding and more deaths, not less, so perfect for the greenie brigade. The excessive copper use would also mean going to ali, so lots more fires.

Electrical fires cause far more deaths than shock. One could in principle include either AFCIs or a heat sensitive resistive composite wire run along all conductors plus a basic bit of electronics. When temp rises unacceptably the thing switches off. Its all gobbling resources though, resources that would be far more constructively be spent elsewhere. At this time going higher V would make more sense than lower.


NT

On 28/07/14 08:27, Nightjar "cpb"@ insert my surname here wrote:
On 28/07/2014 08:13, Tim Watts wrote:
On 28/07/14 02:19, Nightjar "cpb"@ insert my surname here wrote:
On 28/07/2014 01:23, Dave Liquorice wrote:
On Sun, 27 Jul 2014 23:46:14 +0100, Tim Watts wrote:

If I move into very hypothetical areas, I could possibly see a
move to
have residential areas supplied at 50v or less, under the elfen
safety
banner.

That's going to be a big cable to my 3kW kettle and heater ;-)

Even bigger for 10 kW of storage heating... 40 odd amps at 230 V for
a few hours makes the tails warm. The 200 A required for a 50 V
supply is getting hard to handle.


For a H&S viewpoint, an ELV domestic system would save around 20-25
domestic deaths and around a third of a million serious injuries from
electrocution every year.


How many would then die from fires caused by wiring problems?

The biggest cause of electrical fires is overloading of circuits. As we
are not upgrading any existing system, but are starting from scratch and
designing everything anew, with the benefit of present knowledge, we
could build everything to accept heavier overloads and to have much
greater and localised integral overload protection. The result could
well be a reduction in deaths from electrical fires.


And these for sockets:

https://www.google.co.uk/shopping/pr...14369083997541

On 28/07/14 09:50, Nightjar "cpb"@ insert my surname here wrote:
On 28/07/2014 09:47, Andy Burns wrote:
Tim Watts wrote:

High current = larger cables that are more difficult to terminate
properly.

and much more expensive, so people are likely to scrimp and use
under-specced extensions ...



The logical extension of those arguments is to put 11kV straight into
the house :-)


Not really - then it becomes equally dangerous and impractical.

I would say we might as well have 400V as 230V and more or less halve
the conductor sizes. Much more than that is getting silly though.

The logical extension of those arguments is to put 11kV straight into
the house :-)

Aren't we allowed to score more Darwinian selection as a benefit?

--
Robin
reply to address is (meant to be) valid

Well the higher the frequency the more efficient transformers are, and can
be smaller as witnessed by switch mode supplies.
I think for distribution reasons, the delivery would still be AC though.
As a matter of interest, those who use the high voltage DC grids, how do
they convert to AC when needed. have to be one large inverter!

Brian

--
From the Sofa of Brian Gaff Reply address is active
"David Paste" wrote in message
...
Hello all.

The world has a few differing domestic electrical standards, 100, 120,
240 volts, 50 and 60 Hz and so on. Industrial customers have yet more.

Distribution via high voltage AC, and now DC in places.

I understand why various areas of the world have these differences - due
to historical reasons, etc.

My question is that if we were to have a brand new electrical system,
common to all areas, what would, or could, it be? Still AC? 300 volts?
Different frequency?

No real reason to ask other than idle curiosity.

Thanks in advance,

David Paste.

That is the number of deaths and serious injuries in the UK every
year. Around 2.5 million people in the UK also receive a mains voltage
electric shock every year.

Figures from an Electrical Safety Council surveys which have long left
me a bit puzzled. As regards the 2.5m electric shocks, family etc I've
asked (who include people in work and retired, people with young
children, people in rented accommodation etc) don't seem to get shocks
at that rate. So I wonder who/where they are. And as regards "serious
in jury", they define that to include "severe pain" (and all whether or
not medical treatment required).


--
Robin
reply to address is (meant to be) valid

On Sun, 27 Jul 2014 23:49:49 +0100, Tim Watts wrote:

I thought it was more the issue that you cannot phase lock France and
the UK?

No real reason why you couldn't make the channel link work using AC, there are a
number of transmission lines, some with part undergrounded sections in the UK
that are significantly longer overall. No true underwater AC connections
though, the ones that do run underwater (on the grid system at least) all run in
tunnels.

However, the impact of a single point connection and the loss of that connection
was more of a concern, hence the UK - France link is comprised of 2 x 1000MW
links and the AC/DC conversion process permits presettable defined levels of
power transfer regardless of most external conditions so the interconnector is
essentially despatchable 'generation' at the entry point to the respective
countries.

There is also a degree of isolation from system disturbances when
interconnecting at DC which can be very useful from a system stability point of
view.

--

On Mon, 28 Jul 2014 08:16:50 +0100, "harryagain"
wrote:

Our main link to Europe is not underwater, it is via the channel tunnel.
http://www.independent.co.uk/news/bu...l-2289665.html

The two HVDC links to Europe, the 1000MW UK-NED and te 200MW UK-FRA are both
partly underwater, the latter in operation for the last 28 years. Neither use
any part of the channel tunnel.


--

On Sun, 27 Jul 2014 22:33:37 +0100, "Nightjar \"cpb\"@" "insert my surname
here wrote:


Like the man says, although the problem is significantly greater under
water. 30km is about the limit for AC transmission under water, which is
why our links to the continent are HVDC. Even then, the cables are very
specialised and there are IIRC only three manufacturers of HVDC
underwater cables in the world. That is a limiting factor on how many
offshore wind farms can be built, as they need HVDC underwater cable,
the manufacturers have a limited capacity and well filled order books,
while increasing capacity is not something that can be done overnight.

Some, but I'm not sure exactly what proportion of UK offshore wind farms have AC
substations located offshore and an AC connection to the existing grid /
distribution network. I can see DC being of use in the truly offshore arrays
that Germany operates that are out of sight and over the horizon but for the UK
wind farms that are located much closer to shore there seems little or no point
in converting to DC.

There is mention in this article clearly implying an AC connection and
interconnection regime for the London Array the biggest of the white elephant
monstrosities to pollute our country.

http://www.theengineer.co.uk/sectors...012971.article

There is a 600kV 2.2GW mainly underwater DC connection currently under
construction between Scotland and the Wirral to carry the output from wind
generation but this is a point to point grid connection with no directly
connected generation.




--

On 28/07/14 10:40, The Other Mike wrote:
On Sun, 27 Jul 2014 23:49:49 +0100, Tim Watts wrote:

I thought it was more the issue that you cannot phase lock France and
the UK?

No real reason why you couldn't make the channel link work using AC, there are a
number of transmission lines, some with part undergrounded sections in the UK
that are significantly longer overall. No true underwater AC connections
though, the ones that do run underwater (on the grid system at least) all run in
tunnels.

However, the impact of a single point connection and the loss of that connection
was more of a concern, hence the UK - France link is comprised of 2 x 1000MW
links and the AC/DC conversion process permits presettable defined levels of
power transfer regardless of most external conditions so the interconnector is
essentially despatchable 'generation' at the entry point to the respective
countries.

There is also a degree of isolation from system disturbances when
interconnecting at DC which can be very useful from a system stability point of
view.


How are you going to phase lock the French Grid to the UK Grid?

The "length" is a red herring...

"Nightjar "cpb"@" "insert my surname here wrote in message
...
On 28/07/2014 08:13, Tim Watts wrote:
On 28/07/14 02:19, Nightjar "cpb"@ insert my surname here wrote:
On 28/07/2014 01:23, Dave Liquorice wrote:
On Sun, 27 Jul 2014 23:46:14 +0100, Tim Watts wrote:

If I move into very hypothetical areas, I could possibly see a
move to
have residential areas supplied at 50v or less, under the elfen
safety
banner.

That's going to be a big cable to my 3kW kettle and heater ;-)

Even bigger for 10 kW of storage heating... 40 odd amps at 230 V for
a few hours makes the tails warm. The 200 A required for a 50 V
supply is getting hard to handle.


For a H&S viewpoint, an ELV domestic system would save around 20-25
domestic deaths and around a third of a million serious injuries from
electrocution every year.


How many would then die from fires caused by wiring problems?

The biggest cause of electrical fires is overloading of circuits. As we
are not upgrading any existing system, but are starting from scratch and
designing everything anew, with the benefit of present knowledge, we could
build everything to accept heavier overloads and to have much greater and
localised integral overload protection. The result could well be a
reduction in deaths from electrical fires.

I don't believe that with the difficulty of terminating the
much thicker cables required with stuff like electric jugs etc.

On 28/07/14 08:19, John Williamson wrote:
On 28/07/2014 01:56, The Natural Philosopher wrote:
On 27/07/14 22:24, newshound wrote:
On 27/07/2014 21:40, wrote:
Nightjar wrote:
AC for simple long-distance transmission...
Except for underwater cables, where it can cause unacceptable
transmission losses.

How does immersing a 11kV AC cable in water increase transmission
losses? This isn't a joke question, I can't see how the medium
surrounding a cable changes the action of the cable itself, other
than cooling effects.

jgh

It's losses in the dielectric, so it applies to underground cables too.
Dielectric losses in air are low.

No it really isn't dielectric losses.


It's capacitive loading.

Exactly.

But the power isn't lost *in* the dielectric, its lost in driving the
current down the wires *to* the dielectric.

The capacitance per kilometre of overhead lines
between cable and ground is low, while the capacitance per kilometre of
underground cables is at least two orders of magnitude higher.

At the lengths of cable used for power distribution, some of the effects
that normally only affect HF signals come into play at 50Hz.



--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On 28/07/14 08:22, John Williamson wrote:
On 28/07/2014 02:03, The Natural Philosopher wrote:
On 27/07/14 22:45, tony sayer wrote:
In article ,
scribeth thus
Nightjar wrote:
AC for simple long-distance transmission...
Except for underwater cables, where it can cause unacceptable
transmission losses.

How does immersing a 11kV AC cable in water increase transmission
losses? This isn't a joke question, I can't see how the medium
surrounding a cable changes the action of the cable itself, other
than cooling effects.

jgh

Inductive and Capactive losses theres some stuff on the AAB website
somewhere;!...

Not sure that induction plays any part..

Transmission lines have a calculable inductance per metre, and as the
length approaches infinity, so does that inductance.

There is a characteristic impedance for transmission lines, which
affects both transmission and losses.


So, having taught grandmother to suck eggs, where is the power loss due
to inductance?

Seek ye here!...


http://new.abb.com/about/technology/dc-portal







--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On Mon, 28 Jul 2014 10:44:43 +0100, Tim Watts wrote:

On 28/07/14 10:40, The Other Mike wrote:
On Sun, 27 Jul 2014 23:49:49 +0100, Tim Watts wrote:

I thought it was more the issue that you cannot phase lock France and
the UK?

No real reason why you couldn't make the channel link work using AC, there are a
number of transmission lines, some with part undergrounded sections in the UK
that are significantly longer overall. No true underwater AC connections
though, the ones that do run underwater (on the grid system at least) all run in
tunnels.

However, the impact of a single point connection and the loss of that connection
was more of a concern, hence the UK - France link is comprised of 2 x 1000MW
links and the AC/DC conversion process permits presettable defined levels of
power transfer regardless of most external conditions so the interconnector is
essentially despatchable 'generation' at the entry point to the respective
countries.

There is also a degree of isolation from system disturbances when
interconnecting at DC which can be very useful from a system stability point of
view.


How are you going to phase lock the French Grid to the UK Grid?

The "length" is a red herring...

How do you phase lock the French grid to the Belgian Grid to the Dutch Grid to
the German one to the Swiss one etc etc. It doesn't in the main involve DC and
at AC it is no real problem.

There is potentially 'as big a problem' with the UK grid system if it splits
during a major disturbance into a two or more islands of load and generation. In
this case (since the late 80's or so) the synchronising systems have an
additional mode where they just sit there primed until the phase angle and
voltage discrepancy falls with certain limits (which are deliberately set wider
than for normal operation) and the breaker then closes, a successful closure
could potentially take a few hours.

As the grid system operator is separate from the generation operator in the UK
there is no generation intervention required as such, just switchgear that can
take occasionally take a bit of abuse and generator governors that can hold a
set point frequency.

P.S. There is a long established 400kV AC link between Spain and Morocco with a
similar distance underwater to the UK - French link.

--

On 28/07/2014 09:21, Huge wrote:
On 2014-07-28, John Williamson wrote:
On 28/07/2014 02:06, The Natural Philosopher wrote:
On 27/07/14 23:49, Tim Watts wrote:
I thought it was more the issue that you cannot phase lock France and
the UK? So DC is a natural choice if you have to re-invert it. And if
you have to do that, might as well transmit in DC too.

Not saying your reason is not a good reason - I just thought it was a
secondary reason to a fairly immutable primary problem.

No. I visited the first link to france at the UK end and the issue is
primarily one of losses

'we can draw an arc for 30 minutes off the capacitance in that cable'

To drive that capacitance takes a LOT of out of phase current and that
suffers resistive losses.

Big ones

The main AC losses are inductive and leakage by capacitance to ground,
not resistive.

That's what they told me when I took a group of trainee electrical
engineers to the site a few decades ago. The guy was actually quite
surprised when none of them could answer the question he asked of why
they did it the way they do, but the coach driver could.

The coach driver had done the tour before ...


No, the coach driver is the son of an electrical engineer who
specialised in the heavy stuff, and had been playing with electronics
since he was about 11 years old.

--
Tciao for Now!

John.

On 28/07/2014 08:23, harryagain wrote:
"The Natural Philosopher" wrote in message
...
On 27/07/14 23:49, Tim Watts wrote:
I thought it was more the issue that you cannot phase lock France and
the UK? So DC is a natural choice if you have to re-invert it. And if
you have to do that, might as well transmit in DC too.

Not saying your reason is not a good reason - I just thought it was a
secondary reason to a fairly immutable primary problem.

No. I visited the first link to france at the UK end and the issue is
primarily one of losses

'we can draw an arc for 30 minutes off the capacitance in that cable'

To drive that capacitance takes a LOT of out of phase current and that
suffers resistive losses.

Big ones


Drivel
Capacitance does not cause any losses.
It does cause phase shift and instability.
When the cable is under load it will actually help with phase shift.
Only resistance causes losses.

Whenever current is passing through any imperfect conductor.

On an AC transmission line, current is constantly being drawn to alter
the voltage across the line capacitance to earth. So the capacitance is
the cause of the resistive losses.

Loading a cable has no effect on the phase shift you mention, unless
that load is reactive, and depending on whether it is inductive or
capacitive, it can then either worsen or improve the situation.

Where exactly is this arc drawn for 30 minutes and for what purpose.?


The arc *can* be drawn by using the DC charge stored in the cable. No
claim was made that it ever had been drawn either deliberately or
otherwise, though it's the kind of trick that installation engineers
have been known to pull as a joke, or that happens when things go wrong
when commissioning plant of this sort.

The greens are planning to use this effect to store energy in their
proposed long distance links for their beloved European renewables
Supergrid, all of which *you* have mentioned here in the past.

Should we add memory loss to your minimal comprehension skills?

--
Tciao for Now!

John.

On 28/07/2014 11:52, The Natural Philosopher wrote:
On 28/07/14 08:19, John Williamson wrote:
On 28/07/2014 01:56, The Natural Philosopher wrote:
On 27/07/14 22:24, newshound wrote:
On 27/07/2014 21:40, wrote:
Nightjar wrote:
AC for simple long-distance transmission...
Except for underwater cables, where it can cause unacceptable
transmission losses.

How does immersing a 11kV AC cable in water increase transmission
losses? This isn't a joke question, I can't see how the medium
surrounding a cable changes the action of the cable itself, other
than cooling effects.

jgh

It's losses in the dielectric, so it applies to underground cables too.
Dielectric losses in air are low.

No it really isn't dielectric losses.


It's capacitive loading.

Exactly.

But the power isn't lost *in* the dielectric, its lost in driving the
current down the wires *to* the dielectric.

You are quite right, of course. But the term "dielectric loss" is the
one which CEGB trainers used to use when lecturing mixed classes of
mathematicians, physicists, and all types of engineer to explain why
pylons were the prefered method of transmission, with underground cables
the least desirable from the viewpoint of efficiency.

It's a convenient if not very precise shorthand.

On 28/07/2014 10:42, The Other Mike wrote:
On Mon, 28 Jul 2014 08:16:50 +0100, "harryagain"
wrote:

Our main link to Europe is not underwater, it is via the channel tunnel.
http://www.independent.co.uk/news/bu...l-2289665.html

The two HVDC links to Europe, the 1000MW UK-NED and te 200MW UK-FRA are both
partly underwater, the latter in operation for the last 28 years. Neither use
any part of the channel tunnel.


Don't confuse him with facts, or it'll all end in tears.

--
Tciao for Now!

John.

On 28/07/2014 11:52, The Natural Philosopher wrote:
On 28/07/14 08:19, John Williamson wrote:
On 28/07/2014 01:56, The Natural Philosopher wrote:
No it really isn't dielectric losses.


It's capacitive loading.

Exactly.

But the power isn't lost *in* the dielectric, its lost in driving the
current down the wires *to* the dielectric.

There is a niggling, and mostly insignificant loss in that the
insulation isn't a *perfect* dielectric, but yes, the main losses are in
the conductors.



--
Tciao for Now!

John.